1. Field of the Invention
The present invention relates to a circuit for compensating an edge of a luminance signal of a video signal processor such as a television set or a video cassette tape recorder (VCR), and particularly to an improved pattern recognition type edge compensation circuit capable of more effectively compensating an edge of a luminance signal without deterioration of a picture quality by recognizing the pattern of an edge of a luminance signal which is sampled and converted from an analog signal into a digital signal and by properly selecting a sampled signal in accordance with a pattern of the recognized edge.
2. Description of the Conventional Art
FIG. 1 is a block diagram of an edge compensation circuit for a conventional video signal processor, which includes a first differential unit 100 for first-differentiating a luminance signal Y of an analog with respect to time, inputted thereto from an input terminal Yin, a second differential unit 101 for second-differentiating a signal differentiated by the first differential unit 100 with respect to time, a delay unit 102 for compensating a delay time between a luminance signal Y of an analog signal which is not applied to the first and second differential units 100 and 101 and a luminance signal Y of an analog which is applied to the first and second differential units 100 and 101, and a subtraction unit 103 for subtracting the luminance signal second-differentiated by the second differential unit 101 from the luminance signal delayed for a predetermined time by the delay unit 102.
The operation of the edge compensation circuit for a conventional video signal processor will now be explained.
To begin with, a luminance signal of an analog as shown in FIG. 2A is respectively inputted to the first differential unit 100 and the delay unit 102 through an input terminal Yin, the first differential unit 100 first-differentiates a luminance signal with respect to time and outputs a predetermined signal having a wave form as shown in FIG. 2B. Thereafter, the second differential unit 101 second-differentiates the luminance signal first-differentiated by the first differential unit 100 with respect to time and outputs a signal having a wave form as shown in FIG. 2C to the subtraction unit 103. Meanwhile, the delay unit 102 delays a luminance signal Y for a time "t" as shown in FIG. 2D so as to compensate a delay time caused by the first and second differential units 100 and 101 and outputs the delayed luminance signal to the subtraction unit 103. The subtraction unit 103 subtracts an output signal of the second differential unit 101 from the luminance signal as shown in FIG. 2D delayed for a predetermined time by the delay unit 102. Thus, a luminance signal Y' of which edge is compensated as shown in FIG. 2D is obtained.
However, the conventional edge compensation circuit has disadvantages in that under-shooting and over-shooting occur in a luminance signal Y' of which edge is compensated as shown in FIG. 2D, so that a picture quality of a luminance signal of which edge is compensated is deteriorated by the above-mentioned under-shooting and over-shooting.